As a virtual technique for a storage device, there is a storage device which creates a pool (a hierarchical pool) using plural kinds of storage devices having different performances (see, for example, Patent Literature 1). In the hierarchical pool, a storage region of a virtual logical volume is allocated in a data unit called a page and a storage device in which the page is arranged is periodically switched according to an access characteristic (I/O number (IOPS), etc.) per unit time in the page unit. Specifically, a storage region of a high-performance storage device (disk device) is preferentially allocated to a page having a high access characteristic. Consequently, compared with a case in which data is allocated from a single type of a storage device in a virtual logical volume unit, in a case in which a virtual logical volume in a hierarchical pool is configured, when a configuration satisfying a performance requirement and a capacity requirement of a system is designed, a necessary capacity of a high-performance storage device decreases and it is possible to reduce storage cost.
As a technique for reducing storage cost, there is a technique for defining an application condition for a pool and removing a volume configuring the pool while the condition is satisfied (a technique for collecting an excess storage region of the pool) (see, for example, Patent Document 2). According to the technique, it is possible to change a configuration to a pool which can satisfy the performance requirement and the capacity requirement at low cost.